Contact lenses 3 - Ocular surface imaging and assessment

Question 1

what are the steps to checking dry eye disease in clinic?

Answer 1

1. History & symptoms (to include triaging questions &
   risk factor analysis)
   Could use dry eye questionnaire (OSDI or DEQ5)
2. Tear meniscus height
3. Tear film stability (FBUT)
4. Ocular surface staining
5. Meibomian gland assessment & expression

Question 2

why should you instil minimum fluorescein when measuring TBUT?

Answer 2

as fluorescein destabilises the tear film

Question 3

what do you use to check staining of the:
-cornea?
-conjunctiva?
-lid wiper?

Answer 3

-fluorescein
-lissamine green (2 separate instillations in large volumes is required)
-combination of the two

Question 4

how much staining is serious for the:
-cornea
-conjunctiva
-lid wiper

Answer 4

• > 5 corneal spots
• > 9 conjunctival spots
• lid margin ≥2mm length &
  ≥25% width

Question 5

how much of the tear volume does the tear meniscus contain?

Answer 5

75-90% tear
volume

Question 6

What are the advantages of measuring tear meniscus height?

Answer 6

• Tear meniscus contains 75-90% tear volume
• Positive correlation with the lacrimal secretion rate
• Can be assessed subjectively or
  objectively
• Height allows diagnosis of severity of ADDE

Question 7

How does tear meniscus height allow for diagnosis of the severity of adde?

Answer 7

• 0.2mm = mild
• 0.1mm = moderate
• 0mm = severe

Question 8

how do you grade MGD and what are they?

Answer 8

via quality and expressibility gradings:

-Quality grading (0-3)
0 = clear
1 = cloudy
2 = cloudy with debris
3 = toothpaste

-Expressibility grading (0-3)
0 = all glands express
1 = 3 to 4 glands
2 = 1 to 2 glands
3 = no glands

Question 9

what technique can you use to assess the health of meibomian glands? what does it involve?

Answer 9

meibography- where Meibographers use infrared light to image the meibomian glands and grade the gland loss

Question 10

how is meibography graded to assess gland loss?

Answer 10

on a scale from 0-4
-degree 0 = 0%
-degree 1 = less than or equal to 25%
-degree 2 = 26% - 50%
-degree 3 = 51% - 75%
-degree 4 = greater than 75%

Question 11

what do you use in clinic to assess and grade the area of meibomian gland loss?

Answer 11

Topcon MYAH

Question 12

give 3 clinical applications for corneal topography

Answer 12

• Contact lens fitting (Rigid corneal lenses, Orthokeratology)
• Diagnosing & monitoring corneal abnormalities and
  degenerations (eg keratoconus)
• Refractive surgery

Question 13

What are the steps of corneal topography?

Answer 13

1. Placido discs are projected onto the corneal surface
2. instrument camera captures reflection of the rings onto the cornea
3. shape and spacing of the reflected rings is analysed to calculate the cornea’s curvature
4. instrument creates colour-coded maps of the corneal shape

Question 14

how can you non invasively assess the tear film?

Answer 14

using topography

Question 15

what are the two topographers at cardiff uni?

Answer 15

-medmont E300
-Topcon MYAH

Question 16

what is corneal topography used for?

Answer 16

to assess the radius of curvature of the cornea and establish the amount of corneal astigmatism ( starting point to select the ideal
radius of curvature of a rigid corneal lens)

Question 17

what are the measurements in corneal topography and what do they tell you?

Answer 17

• Flat K & Steep K – the simulated
  keratometry (K) values and angle along the flattest and steepest corneal meridians
• Delta K – displays the difference between the flat and steep K values to indicate the amount of corneal astigmatism

Question 18

what are the steps of how rigid corneal lenses fit?

Answer 18

1. the lens BOZR is selected to align with the corneal surface
2. a thin tear lens is formed beneath the rigid corneal lens
3. fluorescein is used to visualise the tear lens to assess the lens fit
4. this allows interpretation of how the back surface of the lens relates to the cornea

Question 19

indian corner shop

Answer 19

bug bug ding ding £2.99, a packet of crisps and a bottle of vineee

Question 20

compare and contrast keratometry vs topography

Answer 20

-keratometry is a simple, widely available and inexpensive instrument whereas topography is sophisticated, expensive and not widely available
-keratometry only assess central area of cornea (approx 3mm) while topography does sophisticated mapping of the entire cornea
-keratometry is ideal for routine lens fitting whereas topography is good for more complex rigid lens fitting as well as routine fittings as it provides stimulated fluorescein patterns
-keratometry is less useful for diagnosing and monitoring corneal abnormalities whereas topography produces sequential maps which allow for monitoring of disease progression and success of ortho-K

Question 21

what are the 2 types of keratometers?

Answer 21

• one position (Bausch & Lomb type)
  -two position (Javal-Schiotz type)

Question 22

What are the steps for using one position keratometry?

Answer 22

1. clean chin and forehead rest
2. make sure keratometer is off and room lights are on
3. turn eyepiece all the way anti clockwise and then clockwise till just clear
4. set up px at headrest
5. find the cornea using pen torch
   4.instruct px to observe the reflection of their eye
6. use joystick to bring mires into focus
7. when in focus, double ring mire at the bottom whole collapse into a single image
8. Twist the longer knob (LHS) to adjust the horizontal separation of the mires and twist the shorter knob (RHS) to adjust the vertical separation of the mires so the plus and minus signs should now be superimposed
9. rotate the barrel slowly clockwise or anti-clockwise until the plus signs are superimposed

Question 23

how do you read the radius of curvature in one position keratometry?

Answer 23

• Read off from scale inside keratometer
• H corresponds to Horizontal meridian
• V corresponds to Vertical meridian
  outside scale gives you dioptric power of the cornea (dont read this)